CO₂ responsive hydrogel-based high sensitivity Pb²⁺ optical fiber sensor with green and in situ desorption

To address the challenges of membrane damage, secondary pollution, and difficulty of in situ desorption and continuous monitoring caused by traditional chelating agents and acidic eluents, a CO₂ responsive hydrogel functionalized optical fiber sensor (OFS) was developed for green desorption of Pb²⁺. The experimental results demonstrate that the OFS achieved a sensitivity of 0.0735 nm/ppb with a limit of detection (LOD) of 0.89 ppb in the concentration range of 0-200 ppb. Selectivity tests with multiple metal ions confirmed its high specificity for Pb²⁺. In addition, the desorption of Pb²⁺ by CO₂ could be achieved under mild conditions. The desorption rate of the sensor was still more than 95 % after several repeated adsorption-desorption cycles. Mechanistic studies revealed that the non-destructive desorption of Pb²⁺ was realized by CO₂, which triggers protonation/deprotonation of -NH₂ and -N-(CH₃)₂ in the sensitive membrane. The OFS has the advantages of being cost-effective and energy-efficient, providing great potential for trace Pb²⁺ detection in complex aqueous environments.